As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature-treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing a web of laminated packaging material. The packaging material has a multilayer structure comprising a layer of fibrous material, e.g. paper, covered on both sides with layers of heat-seal plastic material, e.g. polyethylene, and, in the case of aseptic packages for long-storage products, such as UHT milk, also comprises a layer of oxygen-barrier material, defined, for example, by aluminium foil, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material eventually defining the inner face of the package contacting the food product.
As is known, such packages are produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging machine itself, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, once sterilization is completed, is removed, e.g. vapourized by heating, from the surfaces of the packaging material; and the web of packaging material so sterilized is kept in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and cut along equally spaced transverse sections to form pillow packs, which are then folded mechanically to form the finished, e.g. substantially parallelepiped-shaped, packages.
Alternatively, the packaging material may be cut into blanks, which are folded on forming spindles into packages, which are then filled with the food product and sealed. One example of the this type of package is the so-called “gable-top” package known by the trade name Tetra Rex (registered trademark).
Once formed, packages of the above type may undergo further operations, such as application of a closable opening device.
The most commonly marketed opening devices comprise a frame defining an opening and fitted about a rupturable or removable portion of the top wall of the package; and a cap hinged or screwed to the frame, and which is removable to open the package. Alternatively, other, e.g. slidable, opening devices are also known to be used.
The rupturable portion of the package may be defined, for example, by a so-called “prelaminated” hole, i.e. a hole formed in the fibrous layer of the packaging material before it is covered with the barrier layer, which thus remains whole and closes the hole to ensure airtight, aseptic sealing, while at the same time being easily rupturable.
In the case of aseptic packaging machines, the opening devices described are normally applied continuously, straight onto the formed packages, by on-line applicator units downstream from the packaging machine.
Applying the opening devices, e.g. by heat sealing or gluing, involves various preparatory operations on both the package and opening device. More specifically, when heat sealing the opening device to the package, both the opening device and the heat-seal outer layer of the packaging material surrounding the rupturable portion of the package are preheated to produce partial melting or local softening.
Once applied to the package, pressure must be applied to hold the opening device on the package long enough for the contacting materials to cool and adhere.
Similarly, when gluing the opening device to the package, one or both of the parts being glued must be coated with a layer of adhesive, and then held firmly contacting each other long enough for adhesion to take place.
EP-A-1 215 124, EP-A-1 215 143 and EP-A-1 215 144 describe opening device applicator units, which substantially comprise a continuously-rotating carousel conveyor for conveying the packages from a loading station to an unloading station, and the opening devices from a feed station to an application station interposed between the package loading and unloading stations, and where the opening devices are applied to the respective packages.
More specifically, the carousel conveyor is fitted integrally with a number of seating devices for housing respective packages, and which travel continuously along a circular path extending successively through the package loading station, a localized-heating station for heating around the rupturable portion of the packages, the opening device application station, and, finally, the package unloading station.
The carousel conveyor also comprises a number of applicator devices, each associated with a respective seating device, and which also travel along a circular path over the path of the seating devices.
The opening devices are fed to the respective applicator devices at the feed station, and are fed by the carousel conveyor through a number of heating stations before reaching the application station where they are applied to the respective packages.
Being much thicker than the outermost layer of the packages, the opening devices take much longer to heat than the packages.
Which is why, as compared with the packages, the opening devices call for more heating stations, and must be kept much longer in each.
In the applicator units in the above patents, the problem has been solved by moving the carousel conveyor, and the seating devices integral with it, at constant speed along the relative path, and by connecting the applicator devices to the carousel conveyor by means of variable-speed feed assemblies controlled by a cam system.
More specifically, the feed assemblies provide for feeding the applicator devices in steps at the heating stations, so that the opening devices are kept at the heating stations as long as possible, and for feeding the applicator devices integrally with the carousel conveyor along other portions of their path, and particularly downstream from the application station, where the applicator devices must ensure firm contact between the packages and the opening devices to allow the heat-seal material to cool and so achieve adhesion.
Applicator units of the type briefly described above have various drawbacks.
In particular, the carousel conveyor for both conveying the packages and applying the opening devices is extremely complex and expensive, mainly owing to certain operations, in particular heating of the opening devices, being of minimum duration, which is incompatible with the time taken by the carousel conveyor to travel through a fixed station, so that complex mechanisms are required to release at least portions of the movement of the applicator devices from that of the carousel conveyor.
Moreover, given the continuous movement of the carousel conveyor, and the fact that, over at least part of their respective paths, the applicator and seating devices must travel jointly to enable the opening devices to be applied to and held firmly on the respective packages, the hold time of the applicator devices at the heating stations can only be maximized by imposing sharp acceleration and braking on nearing and leaving the stations, thus resulting in possible dynamic problems.